Paper coated with a composition comprising pigments and styrene-acrolein polymers

ABSTRACT

Acrolein-styrene polymers have been found effective as coatings in imparting water resistance to pigmented paper. Paper is coated with a dried residue of a composition comprising water, clay, water soluble materials such as polyvinyl alcohol, hydrolyzed polyvinyl acetate, methyl cellulose, and starch; and a polymer formed by the polymerization of by weight: A. from 5 to 60 percent acrolein, B. from 40 to 95 percent styrene, C. from 0 to 40 percent acrylonitrile and D. from 0 to 2 percent acrylic acid.

United States Patent [191 Holty et a1.

PAPER COATED WITH A COMPOSITION COMPRISING PIGMENTS AND STYRENE-ACROLEINPOLYMERS Inventors: David W. Holty, Naperville; George T. Kekish,Chicago, both of I11.

Assignee: Nalco Chemical Company, Chicago,

Filed: Jan. 30, 1973 Appl. No.: 327,980

Related U.S. Application Data Division of Ser. No. 82,065, Oct. 19,1970, Pat. No. 3,733,286.

U.S. Cl. 117/155 UA, 117/156, 117/157, 117/161 UC, 117/161 UH, 117/161UN Int. Cl D2lh l/32 Field of Search 117/155 UA, 156, 117/157, 161 UC,161 UH, 161 UW;

260/l7.4 ST, 17.4 CL, 29.6 B, 17 R, 41 A,

[ Nov. 13, 1973 [56] References Cited UNITED STATES PATENTS 3,162,54312/1964 Wilkins 117/76 P 3,231,538 1/1966 Tsatsos 260/29.7 T 3,282,86611/1966 Pohlemann et a1. 260/8 3,321,422 5/1967 Houff et al. 260/l7.4 ST

Primary Examiner-William D. Martin Assistant Examiner-M. R. LusignanAttorney-John G. Premo et a1.

[57] ABSTRACT 1 Claim, No Drawings PAPER COATED WITH A COMPOSITIONCOMPRISING PIGMENTS AND STYRENE-ACROLEIN POLYMERS This is a divisionalapplication of application Ser. No.

A. from 15 to 50% acrolein;

B. from 41.2 to 76.2% styrene;

C. from 8 to 15% acrylonitrile; and D. from 0.8 to 1.5% acrylic acid.

082,065 filed Oct. 19, 1970 now US. Pat. No. 5 Acrylic acid makes thecoating more adhesive and 3,733,286, patented May 15, 1973.

Styrene-butadiene copolymers have been used for coating paper to impartwater resistance to pigmented paper. It is well known in the art thatpaper is quite frequently coated as a means of improving its receptivityto printing inks, its optical characteristics and over-all appearance aswell as to achieve various other desired properties. The majorcomponents of a paper coating composition are ordinarily a pigment, suchas clay, and a binder which serves to bind the pigment particles to oneanother as well as to adhere them to the surface of the paper.

There has been an increased demand for coated and paper board displayinggreater resistance to water. Such water resistant papers are requiredfor off-set printing, for frozen food containers and labels, and formany other applications where the coating is likely to come in contactwith water or a damp atmosphere.

In the prior art, polyvinyl acetates, polyvinyl acrylates andstyrene-butadiene have been used for paper coating. These coatings werenot entirely satisfactory. There was a need for the development of a newpolymer that would form a more water resistant coating.

OBJECTS It is an object of this invention to provide new polymers thatare useful as adhesives for paper coatings. It is another object toprovide new polymers which are particularly useful in the preparation ofsurface coating compositions. It is a further object to provide polymerswhich are particularly useful for the treatment of fibrous materials,such as cloth, paper, and the like. It is a further object to preparecoated papers displaying an unusually high degree of water resistancethereby permitting the thus coated papers to be utilized in allapplications wherein water or moisture are likely to be encountered.

THE INVENTION New surface coating polymers prepared from stable aqueouslatices of the invention are particularly outstanding for their use inpaper coatings and are the insolubilizing reagents of this invention.These polymers are produced from the monomers of acrolein and styrene.Usually the polymer contains from 40 to 95 percent styrene and from 5 to60 percent acrolein. Preferred embodiments of this invention containacrylonitrile and acrylic acid. Although acrylonitrile and acrylic acidare not necessary for the practice of this invention, theirincorporation into the polymer has been found very effective.Preferably, the polymer contains from 5 to 20 percent acrolein, from 40to 95 percent styrene, from to 40 percent acrylonitrile, and from 0 to 2acrylic acid. Usually the acrylic acid makes up about 1% of thecomposition. Preferred embodiments comprise, by weight of:

A. from to 60% acrolein;

B. from 34.5 to 89.5% styrene;

C. from 5 to 40% acrylonitrile; and

D. from 0.5 to 2% acrylic acid.

Further preferred embodiments comprise, by weight of:

gives stability to the latex. The most preferred embodiment of thisinvention comprises a polymer containing 10% acrolein, 69% styrene, 20%acrylonitrile and 1% acrylic acid. All of the percentages disclosed areweight percent unless otherwise specified.

The acrolein-styrene polymers are a great breakthrough in the art.Although acrolein terpolymers are disclosed in the prior art such as U.S. Pat. No. 3,231,538, polymers containing essentially acroleinstyrenesubstituents useful as surface coatings are unique. The use of acroleinproduces a polymer containing free aldehyde groups. If too large anamount of acrolein is used, for example, over 60% by weight, the amountof free aldehyde groups decreases. This is based on the fact that thealdehyde groups coreact to form cyclic compounds. The presence ofstyrene or other monomers in the polymers acts to separate the aldehydeunits and thus prevent the formation of cyclic rings, such astetrahydropyrane rings. Preferably the polymer contains from 5 to 20% ofacrolein. At this low range of acrolein, the amount of cyclization isminimal.

It should be understood by anyone skilled in the art that acrolein isused generically and that other unsaturated aldehydes could be usedwithout departing substantially from the invention. For example,methacrolein, alpha-ethylacrolein, alpha-butylacrolein,alphachloroacrolein, beta-phenylacrolein, alphadecylacrolein,alpha-cyclohexylacrolein and the like could be used.

The acrolein in the polymer acts to insolubilize the coating inconjunction with other ingredients in the coating. The other compoundscontribute other properties to the coating. The acrolein also adds tothe sheer stability, which is an important property.

The polymer reacts with the water-soluble hydroxycontaining material toform the binder. Some of the physical properties that are needed in thebinder are film formation ability, moisture resistance, adhesiveperformance, and printability. Neither the polymer nor the water-solublehydroxy-containing material would work alone. An actual reaction betweenthe two compounds is needed. The binder produced by the reaction of thepolymer and the water-soluble hydroxycontaining material has the desiredphysical properties. The coating that was formed using the compositionsof this invention was tested according to the wet rub and the pickprint-ability tests which will be discussed later.

PREPARATION OF THE POLYMERS The polymers are naturally prepared from themonomers using the specific monomers desired. Following is a typicalsynthesis of the polymer.

EXAMPLE I To a one liter resin kettle was added 500 grams of water, 3grams of sodium lauryl sulfate, and 0.4 grams of ammonium persulfate.Stirring was maintained at 400 revolutions per minute and the nitrogenwas bubbled through the solution for 5 minutes, until foaming becameexcessive. After foaming had subsided, the monomers were added. Themonomers consisted of 15 grams of acrolein and grams of styrene.'Theingredients were mixed. 0.4 grams of sodium metabisulfite was then addedwith 40 grams of water. A slight positive pressure of nitrogen wasintroduced. Five drops of tertiary butyl hydroperoxide was added. Thetemperature was maintained at from 3540 C. for about 3 hours. The latexwas removed to a rotary evaporator for 4 hours. The pH of the materialwas adjusted to 7.8 and the product stored for use.

EXAMPLE II The same steps were followed as in Example I except thatinstead of adding just acrolein and styrene, acrylonitrile and acrylicacid were also added so that the final product contained 10% acrolein byweight, 69% styrene by weight, 20% acrylonitrile and 1% acrylic acid.

EXAMPLE III One liter resin flask equipped with reflux condenser,mechanical stirrer and thermometer was evacuated and purged withnitrogen. 2 grams of sodium lauryl sulfate dissolved in 200 ml ofdeionized water and 1 gram of acrylic acid were added to the resinflask. Then 10 g. of acrolein, inhibited with 100 ppm of hydroquinoneand 89 grams of styrene were added to this mixture with sufficientstirring to produce a good emulsion. After 5 minutes, 0.2 grams ofsodium metabisulfite dissolved in 7.0 ml of deionized water were addedand after three minutes 0.04 grams of tetrabutyl hydroperoxide toinitiate the polymerization.

The reaction was exothermic and the temperature was kept at about 40 c.by means of external cooling. After 2 hours the latex was cooled, andvacuum applied to remove traces of unreacted monomers. The final latexcontained 33% solids. The yield was 98%.

EXAMPLE IV The same as Example III, except amount of monomers was:

1 g. acrylic acid g. acrolein 69 g. styrene g. acrylonitrile The yieldwas 97%.

EXAMPLE V The same as Example Ill, except the amount of monomers was:

1 g. acrylic acid 10 g. acrolein 79 g. styrene 10 g. acrylonitrile Theyield was about 99%.

EXAMPLE VI The same as Example III, except the amount of monomers was:

1 g. acrylic acid 15 g. acrolein 84 g. styrene The yield was about 100%.

EXAMPLE VII The same as Example III, except the amount of monomers was:

2 g. acrylic acid 10 g. acrolein 88 g. styrene The yield was 97%.Various ratios of different mixtures of the monomers and differentpercentages were also run.

COATING The coating is formed by mixing the inert mineral pigment, awater-soluble hydroxy-containing material, and the polymer. The pigmentis usually clay and is about a dispersion. The water-solublehydroxycontaining material is dispersed in water by thorough mixing andcooking. The water-soluble hydroxycontaining material is usually about a20% dispersion. The polymer is made up as a 2050% aqueous suspension,but preferrably 40-50%. These three ingredients are blended together togive an aqueous suspension containing about 20 to 65% by weight solids.The ratio of clay to water-soluble hydroxy-containing material topolymer on a solids basis is usually about 100:8:8.

The water-soluble hydroxy-containing material may be anypolyhydroxy-containing water-soluble material, such as polyvinylalcohol, hydrolyzed polyvinyl acetates, methyl cellulose, and the like,and particularly starches and starch derivatives.

The term "starch includes any amylaceous substance such as untreatedstarch, as well as starch which has been treated by chemical or othermeans to produce oxidized, dextrinized, hydrolyzed, esterified oretherified derivatives of starch so long as the product is stillessentially amylaceous in nature and still contains hydroxyl groupscapable of reacting with reagents. The starches may be derived from anyplant sources, including corn, high amylose corn, waxy maize, sorghum,tapioca, potato, wheat, rice and sago.

The inert mineral pigments which are applicable for use in our novelpaper coating compositions may be selected from among any of the pigmentmaterials which are ordinarily employed in paper coatings. Thus, one mayemploy such well known pigments as kaolin clay, calcium carbonate, andtitanium dioxide. The latter pigments, as well as any others whosepresence is desired by the practitioner, may be utilized either alone orin combination with one another.

The actual application of our novel paper coating compositions to apaper or paperboard substrate may be accomplished by any meansconvenient to the practitioner Thus, for example, one may utilize suchcoating methods as the air knife, roll coater, wire wound rod, trailingblade and size press, etc. Following the application, the resultingcoatings should be dried to cure the coated paper in order to effect thedesired reaction between the water-soluble hydroxy-containing materialand the disclosed polymer. It is this reaction which actuallyinsolubilizes the water-soluble hydroxycontaining material and thusmakes possible the high degree of water resistance displayed by theresulting coatings. The polymer reacts with the starch to form thebinder. In curing the thus coated paper, it may be merely stored atambient temperatures for a period of from 1 to 7 days. On the otherhand, the cure may be accelerated by heating the paper in the driersection of the paper coater. Curing may also be accelerated by additionof appropriate catalysts which act as curing agents. Typical curingagents could be acid or caustic, and many other agents known to thoseskilled in the art.

TEST OF COATINGS In order to test the coatings formed by thecompositions of this invention, the wet-rub and pick printability testswere used.

The wet-rub resistance of the paper which has been coated was determinedby a modification of test procedure RC-l84 of the Technical Associationof the Pulp and Paper Industry (TAPPI). This wet-rub resistance test isused to measure the resistance to the rubbing off of the coating afterthe latter has been moistened. Thus, the coated paper is subjected torubbing under controlled conditions of pressure and wetting and theamount of coating which is removed from the paper is indirectly measuredby turbidometric means such as a photometer. In this series of tests, a2 inch square of the coated paper was used. The paper square was placedin 25 mls. of water for 1 minute. The paper square was then rubbed 20times in one direction in a petri dish. The cloudy water was poured offinto a cell and the transmittance was measured in a spectrophotometer.The transmission was then read. Naturally, the clearer the solution, thebetter. A reading of would be the best.

The other test that was used was the IGT Pick Printability suggestedtest method T-499 of the Technical Association of the Pulp and PaperIndustry (TAPPI). A machine is used to measure the ability of the coatedsurface to withstand the printing process. Picking is the phenomenon oftacky ink pulling the coating away from the surface. This is detected bythe appearance of white dots along the black ink line. The results aremeasured in feet per minute. Naturally, a larger measurement means thatthe coated surface has great durability for the printing process.

The results of various coating formulations are given in the followingtables.

TABLE 1 Weight Acrolein-Styrene Coating Wet-Rub 0:100 26-29 5:95 9-1410:90 5-8 :85 6-10 :80 11-14 As can readily be seen from Table I, whenacrolein is present in the coating the wet-rub is substantiallyimproved. Preferably, the insolubilizing reagent contains from 5 to 30percent by weight of acrolein.

Table II shows that the insolubilizing reagents of this inventioncompare favorably to the expensive commercial protein latex.

TABLE II IFT [GT PlCK 360' Sx. COATlNG COMPOSlTlON 1 Standard Commercialprotein-latex 2 100 clay: 8 ethoxylated starch:

8 acrolein: styrene: acrylic acid (10:89:1)

3 100 clay: 8 ethoxylated starch:

8 styrene: butadiene: acrylic acid (60:39:1)

4 100 clay: 8 ethoxylated starch:

8 acrolein: styrene: acrylonitrile (10:70:20)

5 clay: 25 calcium carbonate:

8 ethoxylated starch; 8 acrolein: styrene: acrylic acid 9 10:89:1

6 75 clay: 25 calcium carbonate:

8 ethoxylated starch: 8 styrene: butadiene: acrylic acid (60:39:l)

7 75 clay: 25 calcium carbonate:

8 ethoxylated starch: 8 acrolein: styrene: acrylonitrile: acrylic acid(l0:69:20:l)

8 75 clay: 25 calcium carbonate:

16 ethoxylated starch No. 6 ink No. 5 ink WET-RUB 5,4

The coating was applied at a rate of 10 percent by weight of paper.

In summary, compositions consisting of acroleinstyrene copolymers areeffective coatings for pigmented paper. These polymers can also containacrylonitrile and acrylic acid. According to the Wet-Rub and PickPrintability tests, these coatings showed marked superiority overcoatings used in the prior art.

What we claim and desire to protect by Letters Patent is:

1. Paper coated with the dried residue derived from a coatingcomposition comprising water, clay, a watersoluble hydroxy-containingmaterial from the group consisting of polyvinyl alcohol, hydrolyzedpolyvinyl acetates, methyl cellulose, and starch, and an insolubilizingreagent, wherein the ratio of clayzwater-soluble hydroxy-containingmaterialzinsolubilizing reagent is 1002828; said insolubilizing reagentcomprises a polymer formed by the polymerization of by weight:

A. from 5 to 60% acrolein;

B. from 40 to styrene;

C. from 0 to 40% acrylonitrile; and

D. from 0 to 2% acrylic acid.

